The invention relates to a heat storage device having a storage vessel, in which the storage mass is disposed which stores latent heat in the course of its transition from the solid to the liquid state, as well as a heat carrier liquid circuit, by means of which the stored heat is fed to the heat emitting element.
Heat storage devices having storage masses are known, which are capable of storing heat in the course of their transition from the solid to the liquid aggregate state. Heat is withdrawn from these heat storage devices by employing as a heat carrier liquid a liquid which is immiscible with the liquid storage mass and which is pumped directly through the storage mass and then through the heat emitting element. The following disadvantages of this arrangement have become known:
(a) The heat exchange between a heat storage mass and a heat carrier liquid flowing therethrough becomes increasingly difficult owing to the increase in the thickness of the layer of the solidified heat storage mass.
(b) The difference in volume of the storage mass between the molten and the solidified phase causes high mechanical stresses in the structural elements, i.e. the storage vessels and the heat exchangers.
(c) As it discharges, the storage mass solidifies into a single solid body, which presents the heat conduction with a high heat resistance during charging.
The object of the invention is to eliminate these disadvantages. This object of the invention is fulfilled by means of a storage mass and a selected heat carrier liquid which is not or only slightly miscible with the melt of the storage mass and where the specific gravity of the storage mass, differs so considerably from the specific gravity of the melt, that layers are formed, and that a pump or mixer rotor is so arranged in the heat carrier liquid layer, that a vortex is formed, whereby a mixture of the storage mass melt and of the heat carrier liquid is sucked up. What is achieved in this way is that, on the one hand, the solidified heat storage mass is divided into minute spheres and, on the other hand, an intensive heat exchange between the storage mass and the heat carrier liquid is accomplished.
In a first embodiment the heat carrier liquid is disposed above the melt. In a second embodiment the storage mass floats on the heavy heat carrier liquid. In the case of the first embodiment there is provided at the top in the storage vessel, and in the case of the second embodiment at the bottom in the storage vessel, a pump rotor, which produces a vortex. In a third embodiment the heat carrier liquid is disposed between the melt and the solid storage mass; then the pump rotor is disposed between the layers of storage mass. The liquid storage mass penetrates into the vortex of the pump rotor and broken up by the pump rotor into minute droplets which assume a spherical shape on account of the surface tension and which then give off their heat to the heat carrier liquid. After solidification, the small spheres are again moved back into the storage mass layer by gravity and by centrifugal forces. Since the entire interior of the circular cylindrical storage vessel performs a revolving current, the spheres are moreover thrown outwardly, so that that region of the melt which enters the vortex remains free from these small spheres. Converse separation occurs where the melt is heavier than the solid storage mass, as is for example the case with water.
In certain circumstances the pump rotor may be dispensed with for charging. Preferably however it is driven during charging also. Only when sufficient storage mass has been melted, it accelerates the heat exchange and thereby reduces the temperature gradient between the heat carrier liquid and the storage mass, so that the charging can also take place via the heat carrier liquid. For the heat carrier liquid, water may, for example, be considered and for the storage mass, wax. The same invention may, however, also be applied in relation to salt melts, particularly hydrates of metal salts. Chlorinated hydrocarbons which are heavier than the salts or hydrocarbons such as benzene, light oil, silicone oil, ketones, cyclohexane, toluol or xylol, which are lighter than the salts, may then, for example, serve as the heat carrier liquid. Where water is used as the storage mass, silicon oil may be considered as the heat carrier liquid.
The pump rotor produces a whirl. Furthermore it has the effect of causing mechanical diminution of the storage mass which has been sucked up. Moreover it effects rotation of the contents of the storage vessel. This rotation can be enhanced by tangential introduction of the return flow of the heat carrier liquid from the exterior heat exchange circuit, so that the separation of solid storage mass, liquid storage mass and the heat carrier liquid takes place in the centrifugal force field, whereby heat storage mass can, in the region adjacent to the axis, be prevented from being taken along into the exterior heat exchange circuit.
Volume equalisation is achieved by an elevated container or an elastic displacement device communicating with the heat carrier liquid.